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Identity Name that uniquely identify an entity –E.g., your SSN Identifier properties: –An identifier refers to at most one entity –Each entity is referred to by at most one identifier –An identifier always refers to the same entity (i.e., it is never reused)

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Internet Centric View Addresses: –Says how to reach an object  it has location semantics associated to it –Usually, a format easy to process by computers Name: –Does not have any location semantics associated to it –Usually, a format easier to understand/read/remember by people Examples: –IP address: –Name: arachne.berkeley.edu

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Name Service Name space: define the set of possible names and their relationship –Hierarchical (e.g., Unix and Windows file names) –Flat Bindings: the mapping between names and values (e.g., addresses or other names) –Bindings can be implemented by using tables Resolution: procedure that, when invoked with a name, returns the corresponding value Name server: specific implementation of a resolution mechanism that is available on the network and that can be queried by sending messages

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Mapping Multiple names can map onto the same address –Example: and arachne.berkeley.edu maps to the same machine (i.e., the same IP address) One name can map onto multiple addresses –Example: can be mapped to multiple machines

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Name Space A general naming graph with a single root node directory node Named entity

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DNS Hierarchy (2) Unique domain suffix is assigned by the Internet Authority The domain administrators have complete control over the domain No limit on the number of subdomains or number of levels Name space is not related with the physical interconnection Geographical hierarchy is allowed (e.g., cnri.reston.va.us) A name could be a domain or an individual objects

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Server Hierarchy Server are organized in hierarchies Each server has authority over a portion of the hierarchy –A single node in the name hierarchy cannot be split –A server maintains only a subset of all names –It needs to know other servers that are responsible for the other portions of the hierarchy

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Server Hierarchy Authority: each server has the name to address translation table for all names in the name space it controls Every server knows the root Root server knows about all top-level domains

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DNS Name Servers No server has all name-to-IP address mappings Local name servers: –Each ISP (company) has local (default) name server –Host DNS query first go to local name server Authoritative name servers: –For a host: stores that host’s (name, IP address) –Can perform name/address translation for that host’s name

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DNS: Root Name Servers Contacted by local name server that can not resolve name Root name server: –Contacts authoritative name server if name mapping not known –Gets mapping –Returns mapping to local name server ~ Dozen root name servers worldwide

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DNS Example Root name server: May not know authoritative name server May know intermediate name server: who to contact to find authoritative name server? requesting host whistler.cs.cmu.edu root name server local name server mango.srv.cs.cmu.edu authoritative name server ns1.berkeley.edu intermediate name server (edu server) 7 8